Dryers and method of operation

ABSTRACT

There is disclosed a method and apparatus for drying materials such as pastes and slurries in which the material is coated onto discrete bodies which are fluidized by an upward stream of gaseous drying agent, the dried material being continuously removed from the fluidized bodies by impacts arising from the motion of the fluidized bodies.

United States Patent Huthwaite 51 May 16,1972

[54] DRYERS AND METHOD OF OPERATION [72] Inventor: John Alan Huthwaite,Stoke-On-Trent, England [73] Assignee: Calmic Engineering CompanyLimited,

Crewe, Cheshire, England [22] Filed: Aug. 24, 1970 [21] Appl.No.: 66,339

[30] Foreign Application Priority Data Aug. 27, 1969 Great Britainmf...42,662/69 [56] References Cited UNITED STATES PATENTS 2,561,394 7/1951Marshall ..159/4 E 2,193,570 3/1940 Seaton ..34/9 3,112,220 11/1963Heiser,Jr. et a1. ....159/4 E 3,110,626 11/1963 Larson et a1 ..l59/4 EPrimary Examiner-John J. Camby Attorney-Beveridge & De Grandi 57ABSTRACT There is disclosed a method and apparatus for drying materialssuch as pastes and slurries in which the material is coated ontodiscrete bodies which are fluidized by an upward stream of gaseousdrying agent, the dried material being continuously removed from thefluidized bodies by impacts arising from the motion of the fluidizedbodies.

16 Claims, 4 Drawing Figures PATENTEDMM 18 1972 SHEET 1 0F 2 INVENTOR;JOHN ALAN HU H AITE PATENTEUMAY 16 1972 SHEET 2 [1F 2 FIG,4.

INVENTOR: JOHN ALAN Hu'mwmre- BY @Widfl Q4 QM DRYERS AND METHOD OFOPERATION The invention concerns driers and relates more particularly toan apparatus and method for reducing the liquid content of a flowablematerial such as a paste or slurry.

The known process of spray drying wherein a flowable material is allowedto fall in the form of a spray down a tower has the disadvantage that,owing to the large size of the tower necessary to provide efficientdrying, capital costs are considerable and the process is onlyeconomically attractive if large quantities of paste or slurry are to bedried. A spray drying tower also requires a substantial amount ofcleaning.

Filtration processes for the reduction of the liquid content of flowablematerials are generally time consuming.

It is known from French Pat. No. 1483141 to dry a granular material bypassing a stream of air upwardly through a bed of the granular materialto fluidize the bed and bring the granules into intimate contact withthe air stream. This process is clearly applicable only to granularmaterials.

It is also known from British Pat. No. 423934 to coat metal or ceramicballs with slurry and to subject the coated balls to heat treatment in adrying chamber, the dried coatings subsequently being separated from theballs. This process requires complex apparatus with the attendant riskof frequent mal-function.

It is an object of the present invention to provide a method andapparatus for drying pastes, slurries and the like which is not subjectto the above disadvantage.

According to the present invention, there is provided a method ofreducing the liquid content of a flowable material, such as a paste orslurry, in which the material is caused to impinge upon and adhere todiscrete bodies which are held in suspension in an upward stream of agas which serves to efi'ect reduction of liquid content of materialadhering to said bodies.

The invention is further described, by way of example, with reference tothe accompanying generally diagrammatic drawings, in which:

FIG. 1 is a cross-sectional side elevation of a drying apparatusconstructed in accordance with one embodiment of the present invention,

FIG. 2 is a plan view ofa detail ofFIG. 1,

FIG. 3 shows a cup-shaped body which may be used in the apparatus, and

FIG. 4 is a cross-sectional side elevation of a drying apparatusconstructed in accordance with a second embodiment of the invention.

Referring to FIG. 1, a drying chamber is secured within an outer casing12. The lower end of the drying chamber 10 takes the form of an invertedfrustrum of a cone and is closed by a mesh screen 14.

An air inlet 16 is formed at the base of the outer casing 12 and an airoutlet 18 which registers with an opening 20 at the upper end of thedrying chamber 10 is formed at the top of the outer casing 12.

A feed assembly generally designated 20 is supported within the dryingchamber 10 and comprises a vertical feed pipe 22, a number of circularlyspaced outlets 24 and an inlet pipe 26. Arranged above the pipe 22 is areticulate member 28 which is shown in elevation in FIG. 1 and in topplan in FIG. 2. In the illustrated embodiment, the reticulate member 28comprises two coaxial annular portions 30, 32 and spokes 34.

A number of light bodies 36 such as hollow balls of plastics material isloosely contained within the chamber 10. As one alternative to plasticsballs, the bodies contained within the chamber 10 may take the formillustrated in FIG. 3 which shows a cup-shaped body 38 which is closedat one end 40 and open at its other end 42. The use of other lightbodies is possible and is included within the scope of the invention.Furthermore, bodies of several different configurations may be used incombination.

In operation of the apparatus depicted in the drawings a prior heated,dry air stream is passed through the inlet 16 and upwardly into thedrying chamber 10, so that the bodies 36 therein become suspended orfluidized. The inverted frustroconical configuration of the lower end ofthe drying chamber 10 causes the air to rise initially in the center ofthe chamber 10 and to diffuse gradually over the width of the chamber10, the motion of the bodies 36 being constrained by the mesh screen 14and reticulate member 28. The apertures between the annular portions 30,32 and spokes 34 of the reticulate member 28 are sufficiently large topermit the bodies 36 to pass through and then fall back thus preventingan undesirable accumulation of bodies such as would occur if thereticulate member 28 were constructed as a mesh such as 14. To promoteturbulence in the fluidized bodies, one or more additional reticulatemembers such as 28 may be provided. While the bodies 36 are in motion,paste, slurry, or like material is passed into the chamber 10 from theoutlets 24 of the feed assembly 20. The material impinges on the bodies36, adheres thereto and is thereby exposed with a large surface arearelative to its thickness, to the heated, dry air stream and is dried.The dried material becomes detached from the bodies 36 and is carried bythe air stream through the outlet 18 to be separated from the air streamin a conventional manner. The detachment of the dried paste from thebodies 36 is facilitated by the collisions of the bodies 36 with oneanother during their motion.

FIG. 4 shows a drying apparatus having a frustoconical housing 1 securedonto a receiving container 2. The housing 1 is open at its upper andlower ends, the upper open end being covered by a mesh screen 3 and thelower open end being covered by a second mesh screen 4. In the center ofthe second mesh screen 4 is situated an upright cone 5, which isprovided with a small cap 6. A number of plastics balls 14 are looselycontained within the housing 1 between the two mesh screens 3 and 4.

A paste injector 7 is secured in the side wall of the housing 1. Theinjector 7 has a nozzle 8 positioned inside the housing 1 and a hopper 9positioned outside the housing 1, and is provided with an internalpiston 10.

An expansion chamber 1 l is positioned on the upper end of the housing 1and is provided with a plastics mesh filter 12a.

The receiving container 2 is provided with a fine mesh screen 12b andcommunicates with an air supply conduit 13.

In operation of the apparatus depicted in FIG. 4 a prior heated, dry airstream is passed along the conduit 13, into the receiving container 2and upwardly into the housing 1, so that the plastic balls 14 thereinbecome suspended or fluidized. The mesh screens 3 and 4 serve toconstrain the motion of the balls 14. The shape of the housing 1 and theprovision of the cone 5 cause the motion of the balls 14 to be in thegeneral direction indicated by the arrows a. While the balls 14 are inmotion, paste is injected into the housing 1 from the nozzle 8 of theinjector 7 by displacement of the piston 10. The injected paste impingeson the balls 14 and adheres thereto. The paste is thereby exposed with alarge surface area relative to its thickness, to the heated, dry airstream and is dried. The dried paste becomes detached from the balls 14and falls through the mesh screen 4 to be collected in the receivingcontainer 2. The detachment of the dried paste from the balls 14 isfacilitated by the collisions of the balls 14 with one another duringtheir motion. The cap 6 serves to prevent material from accumulating onthe cone 5.

The velocity of the air stream is reduced on passing through theexpansion chamber 11 and the filter 12 removes any solid matter from theair stream before it leaves the apparatus, the expansion chamber 11being of sufficient height to ensure that most of the material entrainedin the air stream is able to fall back under the influence of gravitybefore reaching the filter 12a.

In order to permit removal from the apparatus of dried material, a trayor trolley may be positioned beneath the fine mesh screen 12b and besealed to the apparatus, for example, manually or pneumatically.

Provision may be made, by means, for example, of an area of transparentmaterial comprising part of the side wall of the apparatus, forinspecting internal components of the apparatus and the stream ofmaterial issuing from the outlets 24 or nozzle 8.

It is envisaged that the quantity of liquids other than water, forexample acetone and alcohols which may be vaporized at temperatures inthe order of substantially 70 to 150 C., be reduced in flowablematerials by an apparatus and method according to the invention.

I claim:

1. A method of reducing the liquid content of a flowable material, suchas a paste or slurry, in which the material is caused to impinge uponand adhere to discrete bodies held in suspension in an upward stream ofa gas which serves to effect reduction of the liquid content of materialadhering to said bodies and thereby form on the bodies a layer of driedmaterial which is removed from said bodies by collision between saidbodies, said bodies being formed of a material difierent from said driedmaterial.

2. A method according to claim 1 wherein said gas is heated.

3. An apparatus for reducing the liquid content of a flowable material,such as a paste or slurry, comprising a housing having reticulate topand bottom walls, a plurality of discrete bodies contained within saidhousing, means to pass a gas stream upwardly through said housing at aflow rate sufficient to cause said bodies to be entrained in andsuspended by said gas stream, and means to introduce said flowablematerial into said housing and cause said flowable material to adhere tosaid discrete bodies, whereby said gas stream serves to effect reductionof the liquid content of material adhering to said bodies and therebyform on the bodies a layer of dried material which is dislodged fromsaid bodies by mechanical agitation, the bodies being formed of amaterial different from said dried material.

4. An apparatus according to claim 3 wherein said bodies are hollowshells of plastics material.

5. An apparatus according to claim 3 wherein said bodies are hollowspherical balls.

6. An apparatus according to claim 3 wherein at least one of said topand bottom walls of said housing comprises a mesh screen.

7. An apparatus according to claim 5 wherein said bottom wall comprisesa mesh screen and said top wall comprises a reticulate member havingapertures with dimensions greater than those of said bodies.

8. An apparatus according to claim 7 wherein said reticulate member hasa series of spokes radiating from a central region.

9. An apparatus according to claim 7 wherein said housing is generallycylindrical.

10. An apparatus according to claim 9 wherein said housing has a lowerpart which takes the form of an inverted frustrum of a cone.

11. An apparatus according to claim 3 wherein said housing is generallyfrusto-conical.

12. An apparatus according to claim 11 wherein said bottom wall of saidhousing is provided at the center of its upper surface with an uprightconical member.

13. An apparatus according to claim 12 wherein said conical member has acap.

14. An apparatus according to claim 12 wherein said means to pass a gasstream through said housing includes a relatively fine mesh screenlocated upstream of said housing.

15. An apparatus according to claim 11 wherein an expansion chamber islocated downstream of said housing whereby to lower the velocity of thegas issuing from said housing.

16. An apparatus according to claim 15 wherein a relatively fine meshfilter is located in said expansion chamber.

2. A method according to claim 1 wherein said gas is heated.
 3. Anapparatus for reducing the liquid content of a flowable material, suchas a paste or slurry, comprising a housing having reticulate top andbottom walls, a plurality of discrete bodies contained within saidhousing, means to pass a gas stream upwardly through said housing at aflow rate sufficient to cause said bodies to be entrained in andsuspended by said gas stream, and means to introduce said flowablematerial into said housing and cause said flowable material to adhere tosaid discrete bodies, whereby said gas stream serves to effect reductionof the liquid content of material adhering to said bodies and therebyform on the bodies a layer of dried material which is dislodged fromsaid bodies by mechanical agitation, the bodies being formed of amaterial different from said dried material.
 4. An apparatus accordingto claim 3 wherein said bodies are hollow shells of plastics material.5. An apparatus according to claim 3 wherein said bodies are hollowspherical balls.
 6. An apparatus according to claim 3 wherein at leastone of said top and bottom walls of said housing comprises a meshscreen.
 7. An apparatus according to claim 5 wherein said bottom wallcomprises a mesh screen and said top wall comprises a reticulate memberhaving apertures with dimensions greater than those of said bodies. 8.An apparatus according to claim 7 wherein said reticulate member has aseries of spokes radiating from a central region.
 9. An apparatusaccording to claim 7 wherein said housing is generally cylindrical. 10.An apparatus according to claim 9 wherein said housing has a lower partwhich takes the form of an inverted frustrum of a cone.
 11. An apparatusaccording to claim 3 wherein said housing is generally frusto-conical.12. An apparatus according to claim 11 wherein said bottom wall of saidhousing is provided at the center of its upper surface with an uprightconical member.
 13. An apparatus according to claim 12 wherein saidconical member has a cap.
 14. An apparatus according to claim 12 whereinsaid means to pass a gas stream through said housing includes arelatively fine mesh screen located upstream of said housing.
 15. Anapparatus according to claim 11 wherein an expansion chamber is locateddownstream of said housing whereby to lower the velocity of the gasissuing from said housing.
 16. An apparatus according to claim 15wherein a relatively fine mesh filter is located in said expansionchamber.